Right? I feel like if it smells rancid at 6k that means something. Also if you're changing the filter aren't you a bunch and making a mess anyway? I don't care how broke I am, that's the PITA for me, not the 23 dollar jug of new oil.you really run that oil for 15k? man i had a friend in college that used some fancy 15k mile oil in his ram... I told him i wouldnt but.. hey aint my truck.
that was the main issue i had, even if the oil can last that long before breaking down, your still going to have carbon build in in the oil/ filter.. but i fyou change the filter every 5k ish than maybe that negates that issue.. idk 15 k just seems like a lot of miles on the same oil.